The present invention relates to sensors for producing electrical signals representing the flow of liquid along a passage.
Certain known flow sensors use a rotor having vanes driven by the flowing liquid and a transducer that translates motion of the rotor into electrical output waves or pulses. Such signals are supplied to a counter or other receiving apparatus, the frequency of the signals being a representation of the flow rate. For example, one or more magnets on the rotor are carried past a magnetostrictive device mounted close to the path of the magnet(s), producing output pulses. In another flow sensor, a high-frequency-excited coil of a resonant circuit in an oscillator has been located close to a vaned rotor in a flow passage, where the amplitude of oscillation is varied by dielectric portions of the rotor sweeping into and out of the field of the oscillator coil. Such flow sensors involve objectionable physical complexity. Correspondingly, those flow sensors tend to be somewhat costly, a matter of concern in a competitive market.